Facebook and Google was always about friends family and local before any random and stranger interaction becomes relevant.
Reddit and Lemmy is all about strangers. Oftentimes you dont even want people to know you or care about that. So userbase is way easier to create without feeling as if it was too small.
Facebook started locally and slowly created circles until the entire world found their friends and families and joined themselves
It was funny when I came to work at clients offices with suit except a tshirt instead but still jacket.
My client came in with shorts and tshirt. We sitting next to each other was hilarious. Next time i came in with a mote casual long trousers and tshirt no jacket. My colleagues still came with suits but I stopped